The invention is now described using as an illustrative but non-limiting example a container handling system in a container terminal, such as a port. In the following, operation of a typical container port will be explained to an extent necessary for understanding the operation of the invention.
FIG. 1 shows unloading and loading of a container ship 2 by means of a ship crane 4 when the port is operated by straddle carriers 3. Containers 1 are lifted up from container silos of the container ship 2 by means of a container gripper suspended from ropes of the ship crane 4, and lowered into a desired lane 7 on a quay 5. Next, the straddle carriers 3 pick up containers 1A, 1B unloaded from the ship from the ground and transport the containers to a container depot field. When loading a ship, the procedure is reverse. Then, the straddle carriers 3 bring containers 1C to be loaded from the container depot field and lay them beneath the ship crane 4, into a desired lane 7, wherefrom the ship crane 4 then picks them up and lifts on board the ship 2.
Referring to FIG. 1, a vast majority of international transport of goods takes place by means of containers 1. The containers are standard-shaped transport units in which goods are packed for the duration of transport. Typically, containers come in three different sizes of 20 feet, 40 feet or 45 feet in length. The width of a container is about 2.5 meters. The containers arrive at and, correspondingly, leave a container port transported by a container ship 2, container trucks or container trains. A standard-shaped transport unit makes the goods considerably quicker to handle during different stages of transport, particularly when loading and unloading a container ship, as well as when changing from sea transportation to land transportation and vice versa.
The containers are handled in the container port by particular container cranes 3 which include straddle carriers, Rail Mounted Gantry Cranes or RMG cranes, Rubber Tyred Gantry Cranes or RTG cranes, reach stackers, various fork lift trucks, as well as tractor-trailer combinations. A particular type of a rail mounted gantry crane is a ship crane 4 used for lifting containers to be unloaded from a ship onto a quay 5 and, correspondingly, for loading containers brought to a quay on board a container ship.
The aforementioned straddle carrier, for instance, is capable of moving on its rubber tyres around the port area, picking up containers from the ground or from container stacks, and stacking containers on top of one another or placing a container on a container truck bed or on the ground. When containers are laid down on the ground in the port area, they are typically placed in particular container squares 6 or in separate lanes 7 which are designated e.g. by painting on the ground and named or numbered to enable the locations of the containers to be easily recorded.
A current aim is to automate the container cranes 3 so as to make the work of a container crane operator easier and quicker, or the operator may be completely eliminated from the container handling machine, in which case the container handling machine operates without an operator, unmanned.
If the aim is to facilitate the operator's work, typically, then, some work phase in a work cycle is carried out automatically, controlled by a computer. The aim is then to speed up that particular work phase, to increase accuracy, reliability or safety, or merely to facilitate the operator's work.
If the operator is completely eliminated from the control cabin of the container handling machine and the container handling machine operates unmanned, a significant portion of the work phases of the container handling machine is then carried out automatically, controlled by a digital control device (data processing device, in short “computer”). Work phases which cannot be reliably carried out automatically by a computer may, as is previously known, be carried out by utilizing a particular remote control technique, in which case one or more persons for some time control the container handling machines remote-controllably by means of real-time camera footage and radio connection, for instance. The unmanned control of container handling machines enables considerable savings in costs since it then becomes possible to use a large number of container handling machines by few employees.
Some important tasks to be automated are: a) automatic driving of a container handling machine by following desired paths and b) automation of container records.
As will be understood by one skilled in the art, if a container handling machine is to operate without an operator, the characteristic according to a) is essential since typically most of the work cycle time is consumed by driving the container handling machine in the port area. The characteristic of b) is useful in both unmanned and manned operation.
A common requirement for the automation of characteristics a) and b) is that the location of the container handling machine 3 in the port area has to be known, typically at an accuracy of about 10 centimeters. The present invention facilitates the automation of container handling by enabling the accurate location and travel direction of the container handling machine 3 to be determined in real-time.
Next, reference is made to FIG. 2. First, the container handling machine 1) has to be provided with a positioning system 8 capable of measuring the location of the container handling machine constantly at an accuracy of about 10 centimeters. Second, 2) if the measured location differs from a desired or planned route 17 of the container handling machine, the actuators of the container handling machine have to be controlled such that the container handling machine returns to the desired route 17. Typically, condition 2) is not problematic for the container handling machines 3 as far as implementation techniques are concerned if condition 1) can be met. Condition 1), instead, has proven to be difficult to fulfil by employing the known techniques.
As will be understood by a person skilled in the art, for the sake of safety reasons, an unmanned container handling machine cannot be moved at all by a computer unless the real location or travel direction of the container handling machine is known. If the container handling machine were moved by a computer without knowing the real location or travel direction, a danger would arise of the container handling machine colliding with containers, other cranes or other buildings possibly residing along the planned route. Consequently, an absolute requirement to be set for the positioning system 8 is that the measured location data has to be constant with no interruptions to the location measurement by any external disturbing factor.
As will also be understood by a person skilled in the art, the location and direction data measured by the positioning system 8 has to be delay-free and real-time, since the container handling machine 3, such as a straddle carrier, may move a distance of up to ten meters per second, which means that possible deviations from the desired route have to be detected as soon as possible in order to avoid dangerous situations. A measurement frequency typically considered sufficient is about 10 . . . 20 location measurements per second.
As was stated above, another use for the positioning system 8 of a container handling machine according to the invention is associated with automation of container records and automatic monitoring of the location of containers in a port area. After a container 1 has been unloaded from a ship 2, a container handling machine (either controlled by a person or under automatic control by a computer) takes the container to a particular container depot field wherein the containers are typically placed in rows and stacks. The container rows and single container storage places 6 or container squares 6 thereof (cf. FIG. 2) are typically painted on the ground and designated such that each container square may be unambiguously identified and thus the container squares separated from one another in the container records. The single containers are stacked on top of one another in these squares. The location of each single container (typically the identifier of a container square and height in a stack) in the depot field is stored in a particular container Terminal Operating System or TOS provided with an appropriate database. The aim is currently to automate the monitoring of the location of a container in each phase of the handling in order to avoid problems caused by human errors, particularly those made by the operators of the container handling machines 3. If in the depot field the operator of the container handling machine takes the container 1 to a location 6 different from what is assumed by the TOS or, alternatively, the operator of the container handling machine enters into the TOS an erroneous location of the container, it will be problematic to find the container in the container depot field later. In particular, if the container has to be looked for in the depot field while a ship is being loaded, the costs become very high because the aim is expressly to minimize the unloading and loading times of ships in ports.
The prior art enables the location of a container in the container deposit field to be monitored e.g. by using satellite positioning technology (GPS) when no large structures, such as cranes or buildings, are present in the area to interfere with propagation of GPS signals. In such a case, the container handling machine 3 is accordingly provided with a GPS receiver antenna 12 and GPS apparatus for monitoring the location of the container handling machine at intervals of 1 second, for instance. Further, by electrically monitoring the operations of twist-locks of the container handling machine 3, it is possible to detect instances of grabbing a container and leaving a container in a container stack or on the ground at a given moment. As it is naturally assumed that the container 1 does not move without some container handling machine 3 moving it, it is thus possible to monitor the location of the container as long as the container handling machine moves in an open area, within the coverage area of GPS positioning satellites.
However, the GPS positioning technology does not work reliably within the entire port area since the GPS device antenna 12 has to maintain visual communication typically to at least five GPS satellites simultaneously in order to be able to calculate a location reliably. Large container cranes 3, such as a ship crane 4, prevent GPS radio signals from propagating therethrough free of interference, thus causing shadow areas and a decrease in accuracy in the GPS positioning. As the container squares 6 may be located side by side at a distance of about the width of a container, i.e. 2.5 meters, from one another, the accuracy of the GPS positioning should be considerably more accurate than this in order for a container square 6 or a drive lane 7 to be determined correctly. For instance, it is impossible for the GPS technology to reliably detect in which location or in which lane 7 in particular (cf. FIG. 1) beneath a ship crane the container handling machine 3 leaves a container, or from which lane the container handling machine picks up a container. A similar problem occurs when GPS positioning is used in the vicinity of or beneath other large container cranes 3 (e.g. RTG or RMG cranes).
When unloading a ship, for instance, a particular problem is presented by a situation wherein more than one container has been laid onto the ground on the quay, e.g. in adjacent lanes, by the ship crane 4. In FIG. 1, the containers 1A and 1B, for instance, present such a situation. If no positioning data from the container handling machine is available, it is then impossible to know for sure which one of the containers the container handling machine 3 arriving beneath the crane picks up. Consequently, it is also impossible to know for sure in which locations in the container deposit the containers 1A and 1B eventually end up, thus making it impossible to automatically monitor the location of the containers. Similarly, when loading a ship, it is impossible to know for sure in which lane the container handling machine 3 leaves a container. In FIG. 1, a container 1C illustrates this problem. In such a case, it is impossible to automatically ensure that the container 1C becomes loaded correctly on board the ship.
Of course, it is possible that when unloading and loading a ship, someone is arranged on the quay 5 to oversee the operation and e.g. to ensure that the container handling machines 3 and the ship crane 4 pick up the correct containers. However, this phase is subject to human errors which, by means of automation, are to be eliminated. Furthermore, anyone present on the quay is not only an additional cost factor but also a possible presenter of danger situations since accidents happen in ports, even killing people run over by a container handling machine.
EP 0185816 A1, for instance, discloses a technique for positioning a vehicle by means of a laser scanner and retroreflective reflectors. However, the publication discloses no working techniques for positioning a vehicle at all but incorrect conclusions are systematically made from location determination. The techniques of EP 0185816 A1 based on triangulation could work if the directions from the vehicle to the landmarks were absolute directions bound to the ground but, as the vehicle turns with respect to the ground, this is not the case. Since the position of the vehicle is unknown, the techniques of EP 0185816 A1 systematically suffer from the problem that there are more unknown than known factors, making groups of equations—were such presented—impossible to solve.